Electrolyte for Electrochemical Machining

ABSTRACT

The present invention relates to an electrolyte and a process for the electrochemical machining of metallic components, wherein the electrolyte comprises a protic solvent.

The present invention relates to an electrolyte for electrochemical machining, the use of the electrolyte and also a process and an apparatus for electrochemical machining. Electrochemical machining of components allows particularly precise machining of electrically conductive, metallic components. Machining is effected virtually without wear and is particularly gentle on the material. The invention is employed, in particular, in the industrial sector and in the case of large production runs.

Electrochemical machining functions according to the principle of electrochemical removal of material. For this purpose, the component is, for example, connected as the anode and the tool is connected as the cathode. A conductive liquid, also referred to as electrolyte, is pumped through a working gap which remains between the component and the tool. When an electric potential is applied between component and tool, a current flows and initiates electrolysis by means of which metal ions are dissolved from the component. A defined removal of material is achieved in this way. Electrochemical machining enables radii and contours to be produced with great accuracy even at places to which access is difficult. Furthermore, it is possible to machine various positions of the component simultaneously. Since there is no direct contact between the tool and the component, machining occurs with virtually no wear and a very constant process quality is ensured. Furthermore, no mechanical stresses or thermal influences are induced in the component to be machined. Even materials which are difficult to machine by cutting methods can be machined without problems. Owing to short cycle times, which may be up to a few seconds, it is possible to machine relatively large numbers of components with high process reliability. This process is used particularly widely in the after-machining of channels in injection nozzles.

Apart from the numerous advantages mentioned above for electrochemical machining, it has been found in practice that nonuniform surfaces can be formed during the electrochemical machining process. This represents a source of defects in the manufacturing chain because the surfaces produced in this way gave a roughness or structure which can lead to defective functions or failure of the component.

It is therefore an object of the present invention to solve the problems arising from the prior art at least partly and, in particular, to provide a simple and reliable method of carrying out the machining process while simultaneously ensuring a high surface quality.

These objects are achieved by means of an electrolyte having the features of claim 1, a use of the electrolyte according to claim 5, an electrochemical machining process according to claim 6 and an apparatus for electrochemical machining according to claim 9. Further advantageous embodiments of the invention are indicated in the dependent claims. It should be pointed out that the individual features mentioned in the dependent claims can be combined with one another in any technologically useful way and define further embodiments of the invention. In addition, the features indicated in the claims are defined more precisely and explained in the description, with further preferred examples of the invention being presented.

According to the present invention, the objects are achieved by an electrolyte for the electrochemical machining of metallic components, wherein the electrolyte has a proportion of a protic solvent, preferably a protic solvent which is different from water. For the present purposes, an electrolyte for electrochemical machining is a material which is present at least partially in the form of ions in the solid or dissolved state and can conduct an electric current. Such electrolytes include, in particular, liquids which contain ions and can thus conduct a current. Electrolytes which are preferred according to the invention are, in particular, aqueous salt solutions; as aqueous salt solution, it is possible to use, for example, aqueous NaCl solutions or aqueous NaNO₃ solutions in which the salts (NaCl or NaNO₃) are preferably present in a concentration in the range from 30 to 40% by weight.

In electrochemical machining, the electrolyte used flows around at least part of the components to be machined or at least wets the components. It has been found that a nonuniform surface structure is formed during electrochemical machining especially when deposits are present on the surface of the components to be machined. Deposits of greases or oils in particular lead to nonuniform dissolution of the material of the component to be machined. Such contaminants have an effect comparable to that of passivating layers. They prevent dissolution of the metallic material to be removed in the electrolyte. The addition of a protic solvent, preferably a protic solvent which is different from water, to the electrolyte enables these contaminants to be cleaned off in the presence of the electrolyte and uniform removal of the material by dissolution thus occurs. For the purposes of the present invention, a protic solvent is a material which has at least one functional group from which protons can be split off by dissociation in the presence of strong bases. Such protic solvents are able to form hydrogen bonds. The addition of a protic solvent, preferably a protic solvent which is different from water, makes the electrolyte capable of dissolving and transporting away contaminants such as oils and greases. They therefore do not act as passivating layer on the surface of the components to be machined and uniform removal of the metallic material is ensured.

It is advantageous for the average proportion of protic solvent in the electrolyte to be in the range from 0.01 to 80% by volume, particularly preferably in the range from 0.05 to 25% by volume and most preferably in the range from 0.1 to 10% by volume. Depending on the application, e.g. severe or less severe contamination with or adhesion of greases and oils, the electrolyte can be adapted within a wide range in terms of its solvent content to the respective requirements.

For the purposes of the present invention, it is very particularly advantageous for the protic solvent to be a protic polar solvent different from water. Organic solvents having from 1 to 25 carbon atoms, particularly preferably from 4 to 12 carbon atoms, are especially advantageous. The relatively long-chain compounds have still relatively pronounced polar properties and at the same time have very good solvent properties for greases and oils.

In particular, an advantageous embodiment provides for the protic solvent to have at least one functional group selected from the group consisting of a carboxyl group, a carboxylate group, a hydroxyl group and an amino group. Accordingly, the protic solvent is preferably a carboxylic acid, the salt of a carboxylic acid, an alcohol or an amine. As salts of a carboxylic acid, preference is given to using fatty acid salts, in particular soaps, which interact with the electrolyte and can particularly readily clean off greases and oils dissolved therein. The soaps are preferably sodium or potassium salts of carboxylic acids having from 10 to 16 carbon atoms. Alcohols preferred according to the invention can be monools, diols, triols or polyols having more than three hydroxyl groups, with monools, in particular monools having from 1 to 10 carbon atoms, being particularly preferred. Alcohols which are particularly preferred according to the invention are selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol and hexanol, with butanol, pentanol or hexanol being particularly preferred. All the materials or groups of materials mentioned can be used individually or in combination in an electrolyte according to the invention in order to improve its cleaning or grease and oil dissolution action.

In a preferred embodiment of the electrolyte of the invention, the electrolyte comprises an alcohol, preferably a monool. Particular preference is given to a monool having from 3 to 7 carbon atoms in an amount in the range from 0.01 to 80% by volume, particularly preferably in the range from 0.05 to 25% by volume and most preferably in the range from 0.1 to 10% by volume.

The use of an electrolyte according to the invention for the electrochemical machining of metallic components enables a particularly high-quality surface from which material has been removed uniformly to be formed on the components, which is desirable, for example, in the manufacture of very small and highly sensitive components or precision components.

According to the electrochemical machining process claimed for the machining of at least one metallic component, a protic solvent is added to an electrolyte. The addition of the protic solvent can be effected in different ways. The addition can be carried out all at once, e.g. when an electrolyte is initially prepared. However, the protic solvent can also be introduced into an electrolyte stream. This can be carried out continuously or discontinuously.

Thus, an embodiment of the machining process of the invention provides for the protic solvent to be added as a function of a measured concentration of the solvent in the electrolyte. This ensures particularly economical but always precise maintenance of a desired concentration of the solvent over the entire time over which the electrolyte is used. Addition of too much or too little with corresponding adverse effects on the electrochemical machining process is thus effectively avoided.

In the case of particularly strongly contaminated components, it is also advantageous for the component to be machined to be subjected beforehand to precleaning. The precleaning together with the solvent-containing electrolyte ensures that contamination adhering to the component is removed reliably and thoroughly even in the case of particularly severe contamination.

In addition, the objects of the invention are achieved by an apparatus for the electrochemical machining of at least one component, wherein a metering device for addition of a protic solvent to an electrolyte is provided. Such a metering device can continually introduce a small amount into an electrolyte stream and thereby inoculate the latter. Apart from continual or continuous addition, which can be varied in terms of the amount, it is also possible to carry out the addition discontinuously in the form of individual doses introduced separately over time.

For the purposes of the present invention, particular preference is given to providing conduits and transport means which form a circulation system for the electrolyte. In this way, an electrolyte can circulate a number of times and thus also flow a number of times through the machining space and around the component.

It is very particularly advantageous for at least one measurement facility for measuring at least one property of the electrolyte to be provided. Such a property can be, for example, the concentration of the protic solvent in the electrolyte. However, it is also possible to measure further properties such as viscosity, conductivity, temperature or pH of the electrolyte. Furthermore, contamination of an electrolyte can also be monitored by such a measurement facility in order to work up or replace the electrolyte should this become necessary. The installation of a measurement facility is especially advantageous in the context of a circulation system since the life of the electrolyte can be appreciably increased in this way.

Finally, the present invention also provides for the use of a control facility which is connected to the metering device and the measurement facility. The connection is of a process-control nature. That is to say, control signals and/or energy supply lines can be encompassed therein. For the purposes of the present invention, it is important that the control facility can receive the values determined by the measurement facility, determines control instructions for the metering device therefrom and subsequently transmits these to the metering device. This can occur, for example, by transmission of information signals via signal lines. As an alternative, the metering device can also, in particularly simple cases, be activated or deactivated by simple provision of energy via an energy supply line, which can be effected by the control facility.

The invention and the technical context are explained in more detail below with the aid of the figures. It should be pointed out that the figures show particularly preferred variants of the invention but the invention is not restricted to these. The drawing schematically shows:

FIG. 1: an apparatus for electrochemical machining having an electrolyte circuit;

FIG. 2: a contaminated component after electrochemical treatment; and

FIG. 3: a component which has been cleaned according to the invention after electrochemical treatment.

FIG. 1 schematically shows an apparatus 1 for electrochemical machining. This comprises a first reservoir 2 and a second reservoir 3. Furthermore, the apparatus 1 has a machining space 4 in which the components 5 to be machined are arranged between an anode 6 and a cathode 7. An electrolyte 8 flows around the components 5. The electrolyte 8 is conveyed in a clockwise direction by means of transport means 9 formed by pumps through conduit 10 in a circuit 11. During the machining process, the electrolyte 8 takes up metallic material from the components 5 to be machined as a result of the electrolyte dissolving the material in an electrochemical process. The electrolyte 8 then goes via the conduit 10 into the first reservoir 2 from where it is conveyed by the transport means 9 through a filter 12 to the second reservoir 3. In the second reservoir 3, the purified electrolyte 8 is then available for another pass through the machining space 4. The use of an electrolyte 8 having a proportion of a protic solvent, for example an alcohol, ensures that contaminants which may be adhering to the components 5, for instance oil or grease, or dirt, are cleaned off. This is aided, in particular, by the transport means 9 producing a continuous stream of the electrolyte 8 which flows around or through the components 5.

It is particularly advantageous to provide additional flow guides which deflect the electrolyte 8 so that the electrolyte 8 flows around the entire surface to be machined on the component 5. In particular, conduits can be arranged so that the electrolyte is also passed through the components 5. Apart from the depicted use of an electrolyte 8 which is unchanged during the machining process, it is also possible to alter the electrolyte during the machining process by addition of the protic solvent. For this purpose, a metering device 13 which feeds the protic solvent via lines 14 into the electrolyte 8 in the direct proximity of the components 5 is provided in the vicinity of the machining space 4. Due to the direct proximity of the feed conduit or the ends of the feed line 14 to the components 5, a particularly high concentration of the protic solvent 15 can be achieved in the vicinity of the components 5. Associated therewith, it is possible to achieve a particularly high grease dissolution and cleaning action. In addition, the feed lines 14 can be utilized to increase the flow velocity, at least briefly. This can be effected, for example, by introduction of compressed air, of protic solvent 15 or both. A type of flushing of the components 5 is brought about in this way. Apart from the depicted arrangement of the metering device 13 in the region of the machining space 4, the metering device 13 can in principle be arranged at any point in the circuit 11 in order to add the protic solvent 15 to the electrolyte 8. In addition, the metering device 13 can be used together with a control facility 16 which is shown with broken lines and measures the concentration of the solvent in the electrolyte via a measurement facility 17 and be controlled by the control facility 16. For this purpose, the control facility 16 is connected via the control line 18, which is likewise shown using broken lines both to the measurement facility 17 and to the metering device 13.

FIG. 2 schematically shows an electrochemically machined component 5 which is present in a machining space 4 and is surrounded and wetted by the electrolyte 8.

A rough surface 20 with projections 21 can clearly be seen in a channel 19 located in the middle of the component 5. Such a surface 20 is formed during electrochemical machining when the component 5 is subjected, together with adhering greases, oils or other contamination, to electrochemical machining. The depicted projections 21 are then formed at the contaminated places since the contamination acts in a manner similar to a passivating layer.

FIG. 3 shows a component 5 to be machined which is present in a machining space 4 and is likewise surrounded by the electrolyte 8. The electrolyte 8 used here has a proportion of the protic solvent 15 by means of which contamination on the surface 20 of the channel 19 has been cleaned off before or at the latest during electrochemical machining. This makes it possible to produce a particularly smooth surface 20 during electrochemical machining. The projections 21 shown in FIG. 2 are avoided in the case of this component 5 since no passivated areas could be formed as a result of contaminants.

Furthermore, the present invention is not restricted to the examples shown. Rather, numerous modifications of the invention within the scope of the claims are possible. Thus, for example, many protic solvents which are suitable for being conveyed together with the electrolyte in an apparatus for electrochemical machining can be employed instead of the materials described. In addition, the depicted arrangement of the apparatus 1 can be varied to produce many variations without going outside the scope of protection of the present invention.

LIST OF REFERENCE NUMERALS

-   1 apparatus -   2 first reservoir -   3 second reservoir -   4 machining space -   5 component -   6 anode -   7 cathode -   8 electrolyte -   9 transport means -   10 conduit -   11 circuit -   12 filter -   13 metering device -   14 feed line -   15 protic solvent -   16 control facility -   17 measurement facility -   18 control line -   19 channel -   20 surface -   21 projection 

1-12. (canceled)
 13. An electrolyte for the electrochemical machining of metallic components, wherein the electrolyte has a proportion of a protic solvent.
 14. The electrolyte as claimed in claim 13, wherein the average proportion of the protic solvent in the electrolyte is in the range from 0.01 to 80% by volume.
 15. The electrolyte as claimed in claim 13, wherein the protic solvent is a protic polar solvent.
 16. The electrolyte as claimed in claim 13, wherein the protic solvent comprises at least one functional group selected from the group consisting of a carboxyl group, a carboxylate group, a hydroxyl group, and an amino group.
 17. The use of an electrolyte as claimed in claim 13 for the electrochemical machining of metallic components.
 18. An electrochemical machining process for machining at least one metallic component, wherein a protic solvent is added to an electrolyte.
 19. The machining process as claimed in claim 18, wherein the protic solvent is added as a function of a measured concentration of the solvent in the electrolyte.
 20. The machining process as claimed in claim 18, wherein the component to be machined is subjected beforehand to precleaning.
 21. An apparatus for the electrochemical machining of at least one component, wherein at least one metering device for addition of a protic solvent to an electrolyte is provided.
 22. The apparatus as claimed in claim 21, wherein conduits and transport means which form a circulation system for the electrolyte are provided.
 23. The apparatus as claimed in claim 21, wherein at least one measurement facility for measuring at least one property of the electrolyte is provided.
 24. The apparatus as claimed in claim 21, wherein a control facility which is connected to the metering device and the measurement facility are provided. 